Tanning process



Patented Dec. 1933 1,938,388 TANNING rnoosss Alphons 0. Jaeger, MountLebanon, Pa., assignor to The Selden Company, Pittsburgh, Pa., acorporation of Delaware No Drawing.

Application February 27, 1931 Serial No. 518,900

4 Claims. (01. 149-5) This invention relates to the tanning of hides,skins and the like, using a new class of tanning materials.

According to the invention, leather is produced 5 by the tanning ofhides and skins in the presence of a new class of tanning agents, whichmay be used alone or in admixture with other vegetable or artificialtanning materials. The new tanning agents of the present invention arealkali metal salts of the sulfonated products resulting from thecondensation of carbohydrates with sulfuric acid and polymerizedresidues from the vaporization of crude aromatic hydrocarbons such ascrude anthracene, crude naphthalene and the like, by selectivesublimation or distillation.

In these processes the crude hydrocarbons containing, in the case ofcrude anthracene, a mixture of anthracene, phenanthrene, carbazole, deadoils and other high boiling constituents, are subjected to elevatedtemperatures in the presence of solvent gases for long periods of time,

during which the more volatile portions are removed. As aresult, theheavier constituents that remain in the still are highlypolymerized, aspointed out in my prior Patent No. 1,892,770, and to a large extent losetheir original identity and become transformed into tarry masses of highmolecular weight and unknown constitution. By the present inventionthese tars, which have hitherto served no useful purpose, are convertedinto valuable condensation products which are useful for the tanning ofhides into leather. These substances are new chemical products but arenot claimed as such in the present application, this forming the subjectmatter of my copending application Serial No. 512,752, filed J anuary31, 1931.

As is brought out in the application just referred to, these tanningmaterials can be readily prepared from very cheap materials, and arecharacterized by a good light color and excellent tanning properties.They possess rapid penetrating qualities as compared with the vegetabletans and are thus not only valuable tanning agents when used alone butare also well suited for mixture and use with the ordinary vegetable'tans. Being alkali metal compounds, and having a fairly high pH value,they exert a stabilizing action on the ordinary vegetable tanningextracts and prevent them from precipitation by oxidation on exposure tothe air, and they are thus valuable, not only for use as an aid intanning, but also for admixture with the vegetable tans before shipment.

While the stabilizing action and rapid penetration of the novel tanningagents of the present invention make them valuable aids when used inconjunction with the less astringent tanning extracts, such as those ofgambier, oak, chestnut and sumac, these condensation products are ofeven greater value when used in conjunction with the more astringenttans such as quebracho, hemlock, and the like. In the process ofvegetable tanning it is well known that the rate of diffusion, andconsequently the rate of tannage is inversely proportional to theastringency of the tan used. Such extracts as those of quebracho,hemlock, larch, etc. therefore require considerably longer time tocompletely ten the hides than do the less astringent tans such asgambier, probably because the more astringent tans immediately effectsuch a complete tannage at the surface that rapid penetration isretarded. The addition of the tanning materials of the present inventionto the liquors of an astringent vat aids in the penetration, not only byacting as a less astringent diluent, but also by the fact that its morerapid penetration efiects a partial tannage in advance of the vegetableextract, thus preventing imperviousness of the outer portions of thehide.

.The invention is not limited however to the use of the novel tanningagents in conjunction with more astringent tans but on the contrarytheir properties are such that they may be used alone or in conjunctionwith any material having tanning or non-tanning properties.

As has been stated, the tanning agents of the present invention are forthe most part slightly alkaline and usually require the addition ofacids, such asacetic, phosphoric, lactic, etc. to bring the tanningliquors to a value pH=2-5 or thereabouts in order to exert the mostfavorable tanning action. Of course where the tanning agents are used inconjunction with other and more acid materials allowance for this factwill be made 95 and the hydrogen ion concentration will be adjustedaccordingly.

The invention will be further illustrated in con junction with thefollowing examples to which, however, the invention is not limited. Theparts are by weight.

Example 1 50 parts of cellulose in the form of old sulflte paper areintroduced into 750 parts of concentrated sulfuric acid, thoroughagitation and cooling being provided. Thereupon 134 parts of the residuefrom the vaporization of crude anthracene in the catalytic anthraquinoneprocess are stirred in and the stirring continued until all of the resi-110 due dissolves up. The mass is then poured into 10,000 parts ofwater, the excess acidneutralized with lime, fitered, and the calciumsalt transformed into the sodium salt by means of sodium carbonate. 6nevaporating the filtered solution, a brown mass is obtained which is thesalt or" the condensation product. The yield amounts to 173% by weightor the cellulose and anthracene residue.

The hides, delimed and hated, are introduced into a tanning bathcontaining 40 grams per liter of the above described condensationproduct together with suitable amounts of oak bark tanning extract.being allowed to remain with suitable agitation after the tanning actionis well started, until complete tannage is efiected. The leatherobtained after washing and the usual further treatments, is of goodappearance and of excellent strength.

Eacmple 2 50 parts of cellulose in the form of old sulfite paper areintroduced into 750 parts of concentrated sulfuric acid, thoroughagitation and cooling being provided. Thereupon 134 parts of the residuefrom the sublimation of crude naphthalene in the catalytic phthalicanhydride process are stirred in and the stirring continued until all ofthe residue dissolves up. The mass is then poured into 10,000 parts ofwater, the excess acid neutralized with lime, filtered, and the calciumsalt transformed into the sodium salt by means of sodium carbonate. Onevaporating the filtered solution, a light brown mass is obtained whichis the sodium salt of the condensation prodnot. The yield amounts toISO-170% by weight of the cellulose and naphthalene residue.

Hides, properly prepared, are tanned in baths oi the above condensationproduct, the baths increasing in strength as the period oi. tannageproceeds. The pH of the tanning bath is adjusted by the addition ofacetic acid, sodium phosphate being added as a buffer if necessary.

Example 3 50 parts of starch or sugar are introduced into 750 parts ofconcentrated sulfuric acid, thorough agitation and cooling beingprovided. 'I'hereupon 134 parts 01' a residue from the vaporization ofnasaaes semi-purified 60-70% anthracene are stirred in and the stirringcontinued until all of the residue dissolves up. The mass is then pouredinto 10,000 parts of water, the excess acid neutralized with lime,filtered, and the calcium salt transformed the sodium salt by means ofsodium carbonate. On evaporating the filtered solution, a brown mass isobtained which is the sodium or" the condensation product. The yieldamounts to 175% by weight of the starch and anthracene residue.

The above condensation product is admixed with an equal weight of freshquebracho, cats or gambler extract as comes -from the leaching vat, andthe mixture is evaporated to the usual commercial strengths (10-30%moisture content) for sale on the market. The material so produced formsan excellent tanning agent, and precipitation of the vegetable tan byexposure to air, hoth during evaporation and in the preparatien of thetanning liquors, is reduced by the presence or" alkali metal compound.

What is claimed as new is:

l. A process of tanning hides, which comprises treating the hides withan aqueous solution containing at least one salt of a condensationproduct of a carbohydrate, sulfuric acid and the polymerization residuefrom the vaporization of a crude aromatic hydrocarbon.

A process of tanning hides, which comprises treating the hides with anaqueous solution containing at least one alkali metal salt of acondensation product of cellulose, sulfuric acid and the polymerizationresidue from the vaporization of a crude aromatic hydrocarbon.

3. A process of tanning hides, which comprises treating the hides withan aqueous solution containing at least one alkali metal salt of acondensation product of a carbohydrate, sulfuric acid and thepolymerization residue from the vaporization of crude anthracene.

4. A process of tanning hides, which comprises treating the hides withan aqueous solution containing at least one alkali metal salt of acondensation product of cellulose, sulfuric acid and the polymerizationresidue from the vaporization of crude anthracene.

ALPHQNS O. JAEGER.

